The invention is based on a device for optical distance measurement and on a method for optical distance measurement.
Handheld laser distance measuring devices are known that on a top side of their housing have a user input unit with user input or control buttons or keys for activating a distance measurement. In known devices in the prior art, the user input unit for the measuring device comprises a group of keys to which different measurement functions are for instance assigned. The actual measurement function is activated by actuation of a measurement button, which is usually emphasized visually in some way.
In the known optical distance meter known as DLE 30 made by Robert Bosch GmbH, the actual measurement operation is realized—after the device is switched on—by actuation of a double-stroke button. Pressing lightly on the measurement button activates the light source that is integrated with the device, so that the device changes over to a so-called “pointer mode”, in which for a certain period of time, the device emits a continuous, visible laser beam, which can serve to aim at a desired target object. Pressing the measurement button into its second switching position emits a modulated measurement signal of the measuring device, whose returning signal component is detected in the measuring device and evaluated in order to determine the distance between the measuring device and the target object aimed at. The measured value for the distance, ascertained by a control and evaluation unit integrated with the measuring device, is shown in a display of the measuring device.
If the measuring device remains in the “pointer mode” for longer than a predetermined length of time, the control and evaluation unit of the measuring device automatically switches the light source off again. The light source is also switched off once a distance measurement has been performed.
In the laser distance measuring device PD25 made by Hilti, a single key in one user input group is used not only to switch on the device, but also to activate a likewise time-limited “pointer function” by pressing this key again, and to start the actual distance measurement operation by reactuation of this key. Especially in the case of serial measurement, the measurement operation with this device thus requires many key actuations. Moreover, assigning different, multiple functions to one and the same key in a user input element is often the cause of mistakes in user control.